lostplaces-backend/lostplaces/lostplaces_app/models.py

import os
import uuid

from django.db import models
from django.dispatch import receiver
from django.contrib.auth.models import AbstractUser
from django_thumbs.fields import ImageThumbsField

# Create your models here.

class Explorer(AbstractUser):
    """
    Custom user model
    Addtional fields wbd
    """

    def __str__(self):
        return self.username

class Place (models.Model):
    """
    Place defines a lost place (location, name, description etc.).
    """
    name = models.CharField(max_length=50)
    submitted_by = models.ForeignKey(
        Explorer,
        on_delete=models.SET_NULL,
        null=True,
        blank=True, 
        related_name='places'
    )
    location = models.CharField(max_length=50)
    latitude = models.FloatField()
    longitude = models.FloatField()
    description = models.TextField()

    def __str__(self):
        return self.name


def generate_image_upload_path(instance, filename):
    """
    Callback for generating path for uploaded images
    """
    return 'places/' + str(uuid.uuid4())+'.'+filename.split('.')[-1]

class PlaceImage (models.Model):

    SIZES=(
            {'code': 'thumbnail', 'wxh': '390x390'},
            {'code': 'hero', 'wxh': '700x700'},
            {'code': 'large', 'wxh': '1920x1920'}
    )
        
    description = models.TextField(blank=True)
    filename = ImageThumbsField(
        upload_to=generate_image_upload_path,
        max_length=50,
        sizes=SIZES
    )
    place = models.ForeignKey(
        Place,
        on_delete=models.CASCADE,
        related_name='images'
    )
    submitted_by = models.ForeignKey(
        Explorer,
        on_delete=models.SET_NULL,
        null=True,
        blank=True, 
        related_name='images'
    )

    def __str__(self):
        """
        Returning the name of the corresponding place + id 
        of this image as textual represntation of this instance
        """
        return ' '.join([self.place.name, str(self.pk)])



# These two auto-delete files from filesystem when they are unneeded:

@receiver(models.signals.post_delete, sender=PlaceImage)
def auto_delete_file_on_delete(sender, instance, **kwargs):
    """
    Deletes file from filesystem
    when corresponding `PlaceImage` object is deleted.
    """
    if instance.filename:
        if os.path.isfile(instance.filename.path):
            os.remove(instance.filename.path)

@receiver(models.signals.pre_save, sender=PlaceImage)
def auto_delete_file_on_change(sender, instance, **kwargs):
    """
    Deletes old file from filesystem
    when corresponding `PlaceImage` object is updated
    with new file.
    """
    if not instance.pk:
        return False

    try:
        old_file = PlaceImage.objects.get(pk=instance.pk).filename
    except PlaceImage.DoesNotExist:
        return False

    new_file = instance.filename
    if not old_file == new_file:
        if os.path.isfile(old_file.path):
            os.remove(old_file.path)